Integrated Heat Pump Water Heaters
By Tommy Olsen
Over the past 10 years, the water heater industry has seen many advances in technology, delivering higher performance and greater efficiencies: flammable vapor ignition resistance (FVIR), tankless gas, high-efficiency gas units, power direct vent, and enhanced solar products — just to name a few of the innovations.
However, outside of the performance requirements of NAECA II (National Appliance Energy Conservation Act of 2004), little has changed with regard to electric water heaters — until now. Energy-saving, fully integrated, heat pump water heater (HPWH) technology is now readily available, offering more than twice the efficiency of a conventional electric water heater.
While the heat pump concept itself is far from new, the integration of a heat pump, a hot-water storage tank and backup electric elements into the same appliance package is a significant step forward. A new generation of HPWH products incorporates features that boost performance to Energy Star® levels, reducing energy costs and dramatically shrinking a household’s carbon footprint.
But it may surprise you that, even with these advances, the operation of an HPWH is not all that complicated, as compared with that of a conventional unit.
How an integrated HPWH works
Based on the simple principle that cold absorbs heat, an integrated HPWH operates follows a four-step process:
1. Refrigerant, such as R410A, circulates through an evaporator coil and absorbs heat from the atmosphere.
2. The refrigerant is compressed to increase its heat content…
3. … and circulated through a heat-exchange process, where it transfers its heat to the cooler water in the storage tank.
4. Having shed its heat, the cooler refrigerant starts the process all over again.
HPWH design has more in common with your refrigerator than your HVAC (heating, ventilation and air conditioning) system. But to understand the concept of heat pumps, imagine a refrigerator working in reverse:
• A refrigerator removes heat from an enclosed box and expels it to the surrounding air.
• An HPWH takes heat from the surrounding air and transfers it to water in an enclosed tank. Cool air is expelled into the atmosphere.
Myths vs. facts
Heat pump water heating technology remains relatively new and unfamiliar to most contractors and their customers, so misinformation and misperceptions are inevitable. With time and usage, these mistaken ideas will fade. But let’s accelerate the education process by using the rest of this article to take a closer look at 10 of the most prevalent misconceptions:
Myth: A heat pump water heater will replace a home/light residential heat pump air handler.
Fact: A HPWH is designed as a standalone water-heating product. It does not replace your heat pump HVAC system. The two are separate pieces of equipment and serve two distinct functions.
Myth: I’ll have to wait longer for hot water with an HPWH.
Fact: An HPWH performs in the same manner as your current 50-gallon electric water heater, but at less than half the operating cost. For example, with its first hour rating of 67 gallons and a recovery rate of 21 gallons per hour @ 90°F rise in temperature, the Rheem HP-50 Heat Pump Water Heater, for example, requires no lifestyle changes for the consumer. As an added feature, the unit can be set to deliver the same performance as a 65-gallon electric water heater.
Myth: A HPWH is more complicated to install.
Fact: HPWHs require virtually the same installation procedures as any other tank-type electric water heater. The only additional item is a condensate drain connection. That’s because, as an HPWH removes heat from the atmosphere, it generates moisture — or condensate — that must be collected and sent to a drain. This condensate is much like the water droplets that form on a cold drinking glass on a warm day.
Myth: If the HPWH draws moisture from the atmosphere, I don’t need a dehumidifier any more.
Fact: Since an HPWH operates only when there is a demand for domestic hot water — operating no more than four hours daily in a typical home — long-term humidity control is best served by products specifically designed to control humidity.
Myth: HPWHs require specialized maintenance.
Fact: Basic water heater maintenance is pretty much all that is necessary: annual flushing of the tank, periodic inspection of the T&P valve, water and electric connections. The lone additional servicing step involves periodic inspection of a reusable air filter in the heat pump section of the unit. To remove dust and lint buildup, simply wash the filter with a little soap and water.
Myth: A HPWH can be installed in a closet.
Fact: Probably not — unless that closet is a very large, walk-in type. HPWHs require approximately 1,000 cubic feet of ambient (unconditioned air) to operate properly. This is an area measuring roughly 10-foot 5 10-foot 5 10-foot. Ideal installation locations are attics, garages and basements.
Myth: I’ll need to hire an HVAC technician to install and service the water heater.
Fact: HPWHs are delivered as fully charged, sealed systems — just like refrigerators and room air conditioners. As a result, an HVAC technician is not needed in the installation process.
Myth: If it gets too cold, my HPWH won’t have enough warm air to operate.
Fact: Not so. For example, the Rheem HP-50 will continue to draw warmth from the air when the indoor, ambient temperature falls as low as 40°F. Should the indoor temperature at the installed location drop below that level, the HP-50 will continue to supply hot water using two conventional electric elements. Once the ambient temperature rises above 40°F again, heat pump operation will resume.
Myth: I can use my HPWH to cool my attic, garage or basement.
Fact: While operating, a HPWH will emit cool air from the heat exchange process; however, just as your refrigerator will not generate enough heat to warm your kitchen on a cold day, an integrated HPWH will not operate enough hours in a day for long-term cooling benefits
Myth: Heat pumps water heaters are loud.
Fact: The Rheem HP-50 with its whisper-quiet fan operates at less than 49 decibels. Normal conversation is 65 decibels.
Improvements to come
Current HPWH technology is just the beginning, as manufacturers work to maximize water heater performance, energy efficiency and customer payback. As improvements come on stream, you can expect to see units with higher storage capacities, higher kilowatt-hour inputs and even faster first-hour recoveries.
In short, heat pump water heating is a technology whose time has definitely come.
Tommy Olsen is a product manager at Rheem Water Heating in Montgomery, Alabama. He can be reached at: tommy.olsen@rheem.com.